Very obvious trail grew confused (4,5)
I believe the answer is:
writ large
'very obvious' is the definition.
(I've seen this before)
'trail grew confused' is the wordplay.
'confused' indicates anagramming the letters.
'trail'+'grew'='trailgrew'
'trailgrew' anagrammed gives 'WRIT LARGE'.
(Other definitions for writ large that I've seen before include "Emphasised" , "exaggerated" , "on a mass scale" , "very obvious" .)